I could hear some crackling noise coming out of the speakers after turning on the amplifier. I am using a tube amplifier. In fact the noise resembles that of a wire scratching a terminal of a battery just like when you are testing the speaker for sound. I recently purchased 2 crossovers to replace the old crossovers which have been around for over 10 years. I heard the same sound before replacing the crossovers thinking that it was due to the old crossovers. But even after replacing those crossovers, I am still hearing that scratchy sound on the speaker. Sometimes it appears on both speakers and at times just only one side. But strangely enough as I played the system longer, the scratchy noise seems to disappear by itself. This scratchy noise is rather apparent after switching on the amplifier (1-2 minutes) and it can be heard when playing soft music. Any clue? Thank you.
Nothing specific. It could be a tube that's acting up. Power up the amp in a completely dark room and watch the tubes as they come to life. If they spark and glow oddly, then there's a good chance you have a bad tube. Not always though, it could be a bad cap or resistor in line with the tube. You can check by subbing another tube in its place. Always power down a tube amp before you do any trouble shooting and remember to be careful. Voltages tend to be in the 400 to 650VDC range with most tube amps and can still cause a nasty surprise for hours after the amp has been powered down.
Noise from both channels tends to suggest a component or tube which is common to both channels. That would initially narrow the search down to those items found in the power supply. Could be a phase splitter or common driver tube. Or a common to both channels filter cap. If tube substitution doesn't prove successful, then you should contact the amp manufacturer and ask them for advice. DO NOT, UNDER ANY CIRCUMSTANCES, STICK YOUR HANDS INSIDE A TUBE AMPLFIER.
Also, if you don't already know, never power up a tube amp without a load on its outputs. That means you need either speakers or load ressitors connected to the amp whenever it's running.
All of these comments may be in the wrong direction. I'd bet it's a dirty or slightly corroded volume control switch (potentiometer).
Try dis-assembling to get at the volume control switch/potentiometer. Spray a couple S H O R T shots of WD-40 into the volume control pot into a hole or spacing in the V/C pot. YOU DON"T NEED MUCH !!! Let it sit for a few seconds (10 seconds + or -)and start working the volume knob back and forth through the entire range. Do it 30 - 40 times. Blot up any excess WD-40 with a tissue, re-assemble it all, and try that. Many times the variable aspect can pick up cooking oil, dust, or what ever from the air and show scratching or buzz. I've fixed 50 or more speaker noise faults doing this, especially on older 5+ years speaker systems, stereos, and vintage radios. Give it a try before busting go crazy buying stuff or pitching the speakers.
It could be the pot, with this type of amp, it could be a grey cat that walked past it five years ago.
The symptom which would say "not the vc" to me is the op didn't mention this noise occurring when he adjusted the volume level. The noise is there when listening to music, which, to me, says not the vc. That the noise tends to go away as the amp warms up - again, not a vc. The sound is most noticeable when the amp is fired up - again, not a vc.
Unfortunately, without the amp in front of me, I can only guess at the cause. However, given the symptoms as described in the op, I wouldn't make my first bet on a noisy volume control.